1. Field of the Invention
The present invention relates to a method of making the compound CuInSe.sub.2 (CIS) by depositing a precursor of this compound at least partly electrolytically on a substrate and forming the compound CuInSe.sub.2 by thermal reaction.
2. Description of the Prior Art
DE-C2-4103291 discloses a method of making thin films of CuInSe.sub.2 by galvanic deposition of a layer of Cu/In containing Se dispersed in the form of particles in a stoichiometric ratio, followed by a heat treatment to form the compound CuInSe.sub.2, which acts as a photosensitive semiconductor layer which, once covered with a layer of CdS for example, constitutes a photovoltaic diode.
The electrolytic deposition, in particular of the In, has to meet an economic requirement. It is essential that the price/photovoltaic performance ratio be competitive with other means of production of electric energy. It is for this reason that the methods of deposition of all the compounds in the vapor phase which have already been proposed are much too expensive to produce solar cells at competitive prices. In fact, the deposition of In in the vapor phase brings about a condensation of In on the walls of the chamber. The quantity of In thus lost is substantial. Furthermore, In is an expensive metal.
Not only does electrolytic deposition give rise to difficulties in simultaneously depositing the three elements Cu In Se, but in addition, given the extreme reactivity of Se, it turns out that one of the rare substrates more or less able to resist Se at the moment of the formation of the compound CIS is Mo. Every specialist in electrochemistry knows that molybdenum constitutes a substrate on which it is difficult to deposit metals or alloys with an excellent adhesion by galvanic means. Thus copper can only be deposited with relative difficulty on molybdenum by this means and the alloy In-Cu has a very poor adhesion. Furthermore, molybdenum adheres very poorly on glass which generally forms the most common support for photovoltaic cells.
It will thus be realized that if the problem of jointly depositing Cu In Se has been solved, there remain other problems to solve in order to permit the production of photovoltaic cells with a CuInSe.sub.2 film (hereinafter referred to as CIS) obtained at least partially by galvanic deposition.